The large storage capacities and relative low costs of CD-ROMS and DVDs have created an even greater demand for still larger and cheaper optical storage media. Holographic memories have been proposed to supersede the optical disc as a high-capacity digital storage medium. The high density and speed of the holographic memory comes from three-dimensional recording and from the simultaneous readout of an entire packet of data at one time. The principal advantages of holographic memory are a higher information density (1011 bits per square centimeter or more), a short random access time (˜100 microseconds and less), and a high information transmission rate (109 bit/sec).
In holographic recording, a light beam from a coherent light source (e.g., a laser) is split into a reference beam and an object beam. The object beam is passed through a spatial light modulator (SLM) and then into a storage medium. The SLM forms a matrix of shutter (in the binary case) or, more generally, a matrix of photocells modulating the light intensity that represents a packet of data. The object beam passes through the SLM which acts to modulate the object beam with the data input to the SLM. The modulated object beam is then processed by an appropriate optical system and then directed to one point on the storage medium by an addressing mechanism where it intersects with the reference beam to create a hologram representing the packet of data.
An optical system consisting of lenses and mirrors is used to precisely direct the optical beam encoded with the packet of data to the particular addressed area of the storage medium. Optimum use of the capacity of a thick storage medium is realized by spatial and angular multiplexing. In spatial multiplexing, a set of packets is stored in the storage medium shaped into a plane as an array of spatially separated and regularly arranged subholograms by varying the beam direction in the x-axis and y-axis of the plane. Each subhologram is formed at a point in the storage medium with the rectangular coordinates representing the respective packet address as recorded in the storage medium. In angular multiplexing, recording is carried out by keeping the x- and y-coordinates the same while changing the irradiation angle of the reference beam in the storage medium. By repeatedly incrementing the irradiation angle, a plurality of packets of information is recorded as a set of subholograms at the same x- and y-spatial location.
Previous holographic devices for recording information in a highly multiplexed volume holographic memory, and for reading the information out, require components and dimensions having a large size which places a limit on the ability to miniaturize these systems. Because previous holographic devices use motors and large-scale components such as mirrors and lenses, the addressing systems of these previous devices are slow. Furthermore, the mechanical components of these previous devices need frequent maintenance to correct errors and dysfunction coming, for instance, from wear and friction (i.e., tribology effect). Furthermore, previous addressing systems are expensive because they use complex systems for control. Thus, their prices cannot be lowered by mass production. Moreover, previous devices are not economical in their energy consumption. Even when previous addressing devices are accurate when new, the wear and friction of the interacting surfaces that are in relative motion lowers their accuracy with time.
In view of the foregoing, it would be desirable to provide one or more techniques which overcomes the above-described inadequacies and shortcomings of the above-described proposed solutions.
Thus, it is an object of the present invention to provide a dynamic diffractive optics reading system made of solid state components.
It is another object of the present invention to provide an apparatus for reading a diffractive optics memory having components that operate faster than systems produced today.
It is a further object of the present invention to provide an apparatus for reading a diffractive optics memory having components that more accurately target movement of the laser beams onto the recorded regions of the diffractive optics memory.
It is yet a further object of the present invention to provide an apparatus for reading a diffractive optics memory having miniature component sizes.
It is still another object of the present invention to provide inexpensive components for a dynamic diffractive optics reading system.